text: For drinking water, biological water treatment involves the use of naturally occurring microorganisms in the surface water to improve water quality. Under optimum conditions, including relatively low turbidity and high oxygen content, the organisms break down material in the water and thus improve water quality. Slow sand filters or carbon filters are used to provide a support on which these microorganisms grow. These biological treatment systems effectively reduce water-borne diseases, dissolved organic carbon, turbidity and color in surface water, thus improving overall water quality.
  Typically in drinking water treatment; granular activated carbon or sand filters are used to prevent re-growth of microorganisms in water distribution pipes by reducing levels of iron and nitrate that act as a microbial nutrient. GAC also reduces chlorine demand and other disinfection by-product accumulation by acting as a first line of disinfection. Bacteria attached to filter media as a biofilm oxidize organic material as both an energy and carbon source, this prevents undesired bacteria from using these sources which can reduce water odors and tastes [Bouwer, 1998]. These biological treatment systems effectively reduce water-borne diseases, dissolved organic carbon, turbidity and color in surface water, thus improving overall water quality.
  Biotechnological techniques can be used to improve the biofiltration of drinking water by studying the  microbial communities in the water. Such techniques include qPCR (quantitative polymerase chain reaction), ATP assay, metagenomics, and flow cytometry.